Imperial College London

Professor Norbert Hoffmann

Faculty of EngineeringDepartment of Mechanical Engineering

Visiting Professor
 
 
 
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Contact

 

n.hoffmann

 
 
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Location

 

557City and Guilds BuildingSouth Kensington Campus

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Summary

 

Publications

Publication Type
Year
to

129 results found

Fontanela F, Grolet A, Salles L, Chabchoub A, Champneys AR, Patsias S, Hoffmann Net al., 2019, Dissipative solitons in forced cyclic and symmetric structures, Mechanical Systems and Signal Processing, Vol: 117, Pages: 280-292, ISSN: 0888-3270

© 2018 The emergence of localised vibrations in cyclic and symmetric rotating structures, such as bladed disks of aircraft engines, has challenged engineers in the past few decades. In the linear regime, localised states may arise due to a lack of symmetry, as for example induced by inhomogeneities. However, when structures deviate from the linear behaviour, e.g. due to material nonlinearities, geometric nonlinearities like large deformations, or other nonlinear elements like joints or friction interfaces, localised states may arise even in perfectly symmetric structures. In this paper, a system consisting of coupled Duffing oscillators with linear viscous damping is subjected to external travelling wave forcing. The system may be considered a minimal model for bladed disks in turbomachinery operating in the nonlinear regime, where such excitation may arise due to imbalance or aerodynamic excitation. We demonstrate that near the resonance, in this non-conservative regime, localised vibration states bifurcate from the travelling waves. Complex bifurcation diagrams result, comprising stable and unstable dissipative solitons. The localised solutions can also be continued numerically to a conservative limit, where solitons bifurcate from the backbone curves of the travelling waves at finite amplitudes.

JOURNAL ARTICLE

Fontanela F, Grolet A, Salles L, Chabchoub A, Hoffmann Net al., 2018, Dark solitons, modulation instability and breathers in a chain of weakly nonlinear oscillators with cyclic symmetry, JOURNAL OF SOUND AND VIBRATION, Vol: 413, Pages: 467-481, ISSN: 0022-460X

JOURNAL ARTICLE

Koellisch N, Behrendt J, Klein M, Hoffmann Net al., 2018, Nonlinear real time prediction of ocean surface waves, OCEAN ENGINEERING, Vol: 157, Pages: 387-400, ISSN: 0029-8018

JOURNAL ARTICLE

Oberst S, Baetz J, Campbell G, Lampe F, Lai JCS, Hoffmann N, Morlock Met al., 2018, Vibro-acoustic and nonlinear analysis of cadavric femoral bone impaction in cavity preparations, INTERNATIONAL JOURNAL OF MECHANICAL SCIENCES, Vol: 144, Pages: 739-745, ISSN: 0020-7403

JOURNAL ARTICLE

Oberst S, Baetz J, Campbell G, Lampe F, Leis JCS, Hoffmann N, Morlock Met al., 2018, Vibro-acoustic and nonlinear analysis of cadavric femoral bone impaction in cavity preparations, International Conference on Engineering Vibration (ICoEV), Publisher: E D P SCIENCES, ISSN: 2261-236X

CONFERENCE PAPER

Oberst S, Niven RK, Lester DR, Ord A, Hobbs B, Hoffmann Net al., 2018, Detection of unstable periodic orbits in mineralising geological systems., Chaos, Vol: 28

Worldwide, mineral exploration is suffering from rising capital costs, due to the depletion of readily recoverable reserves and the need to discover and assess more inaccessible or geologically complex deposits. For gold exploration, this problem is particularly acute. We propose an innovative approach to mineral exploration and orebody characterisation, based on the analysis of geological core data as a spatial dynamical system, using the mathematical tools of dynamical system analysis. This approach is highly relevant for orogenic gold deposits, which-in contrast to systems formed at chemical equilibrium-exhibit many features of nonlinear dynamical systems, including episodic fluctuations on various length and time scales. Feedback relationships between thermo-chemical and deformation processes produce recurrent fluid temperatures and pressures and the deposition of vein-filling minerals such as pyrite and gold. We therefore relax the typical assumption of chemical equilibrium and analyse the underlying processes as aseismic, non-adiabatic, and inherent to a hydrothermal, nonlinear dynamical open-flow chemical reactor. These processes are approximated using the Gray-Scott model of reaction-diffusion as a complex toy system, which captures some of the features of the underlying mineralisation processes, including the spatiotemporal Turing patterns of unsteady chemical reactions. By use of this analysis, we demonstrate the capability of recurrence plots, recurrence power spectra, and recurrence time probabilities to detect underlying unstable periodic orbits as one sign of deterministic dynamics and their robustness for the analysis of data contaminated by noise. Recurrence plot based quantification is then applied to three mineral concentrations in the core data from the Sunrise Dam gold deposit in the Yilgarn region of Western Australia. Using a moving window, we reveal the episodic recurring low-dimensional dynamic structures and the period doubling route to inst

JOURNAL ARTICLE

Papangelo A, Hoffmann N, Grolet A, Stender M, Ciavarella Met al., 2018, Multiple spatially localized dynamical states in friction-excited oscillator chains, JOURNAL OF SOUND AND VIBRATION, Vol: 417, Pages: 56-64, ISSN: 0022-460X

JOURNAL ARTICLE

Stender M, Tiedemann M, Hoffmann N, Oberst Set al., 2018, Impact of an irregular friction formulation on dynamics of a minimal model for brake squeal, MECHANICAL SYSTEMS AND SIGNAL PROCESSING, Vol: 107, Pages: 439-451, ISSN: 0888-3270

JOURNAL ARTICLE

Tsitoura F, Gietz U, Chabchoub A, Hoffmann Net al., 2018, Phase Domain Walls in Weakly Nonlinear Deep Water Surface Gravity Waves, PHYSICAL REVIEW LETTERS, Vol: 120, ISSN: 0031-9007

JOURNAL ARTICLE

Hadjihoseini A, Lind PG, Mori N, Hoffmann NP, Peinke Jet al., 2017, Rogue waves and entropy consumption, EPL, Vol: 120, ISSN: 0295-5075

JOURNAL ARTICLE

Oberst S, Marburg S, Hoffmann N, 2017, Determining periodic orbits via nonlinear filtering and recurrence spectra in the presence of noise, 10th International Conference on Structural Dynamics (EURODYN), Publisher: ELSEVIER SCIENCE BV, Pages: 772-777, ISSN: 1877-7058

CONFERENCE PAPER

Papangelo A, Ciavarella M, Hoffmann N, 2017, Subcritical bifurcation in a self-excited single-degree-of-freedom system with velocity weakening-strengthening friction law: analytical results and comparison with experiments, NONLINEAR DYNAMICS, Vol: 90, Pages: 2037-2046, ISSN: 0924-090X

JOURNAL ARTICLE

Papangelo A, Grolet A, Salles L, Hoffmann N, Ciavarella Met al., 2017, Snaking bifurcations in a self-excited oscillator chain with cyclic symmetry, COMMUNICATIONS IN NONLINEAR SCIENCE AND NUMERICAL SIMULATION, Vol: 44, Pages: 108-119, ISSN: 1007-5704

JOURNAL ARTICLE

Papangelo A, Hoffmann N, Ciavarella M, 2017, Load-separation curves for the contact of self-affine rough surfaces, SCIENTIFIC REPORTS, Vol: 7, ISSN: 2045-2322

JOURNAL ARTICLE

Grolet A, Hoffmann N, Thouverez F, Schwingshackl Cet al., 2016, Travelling and standing envelope solitons in discrete non-linear cyclic structures, MECHANICAL SYSTEMS AND SIGNAL PROCESSING, Vol: 81, Pages: 75-87, ISSN: 0888-3270

JOURNAL ARTICLE

Hadjihosseini A, Waechter M, Hoffmann NP, Peinke Jet al., 2016, Capturing rogue waves by multi-point statistics, NEW JOURNAL OF PHYSICS, Vol: 18, ISSN: 1367-2630

JOURNAL ARTICLE

Oberst S, Zhang Z, Campbell G, Morlock M, Lai JCS, Hoffmann Net al., 2016, Towards the understanding of hip squeak in total hip arthroplasty using analytical contact models with uncertainty, INTER-NOISE 2016, Pages: 5539-5549

© 2016, German Acoustical Society (DEGA). All rights reserved. Osteoarthritis in hip joints affects patients' quality of life such that often only costly orthopaedic surgeries i.e. total hip arthroplasty (THA) provide relief. Common implant materials are metal alloys, steel or titanium-based, plastics such as ultra-high molecular weight polyethylene, or biocompatible alumina and composite ceramics. Hard-on-hard (HoH) bearing articulations, i.e. ceramic-on-ceramic, or hard-on-soft combinations are used. HoH implants have been known to suffer from squeaking, a phenomenon commonly encountered in friction-induced self-excited vibrations. However, the frictional contact mechanics, its dynamics related to impingement, the effect of socket position, stem configuration, bearing size and patient characteristics are poorly understood. This study gives an overview of the state of the art biomechanical research related to squeaking in THA, with a focus on the effects of friction, stability, related wear and lubrication. An analytical model is proposed to study the onset of friction-induced vibrations in a simplified hemispherical hip stem rubbing in its bearing by varying the contact area. Preliminary results of the complex eigenvalue analysis and stick-slip motion analysis indicate that an increased contact fosters the development of instabilities, even at very small values of the friction coefficient owing to large local contact pressures.

CONFERENCE PAPER

Salles L, Staples B, Hoffmann N, Schwingshackl Cet al., 2016, Continuation techniques for analysis of whole aeroengine dynamics with imperfect bifurcations and isolated solutions, NONLINEAR DYNAMICS, Vol: 86, Pages: 1897-1911, ISSN: 0924-090X

JOURNAL ARTICLE

Akhmediev N, Soto-Crespo JM, Devine N, Hoffmann NPet al., 2015, Rogue wave spectra of the Sasa-Satsuma equation, PHYSICA D-NONLINEAR PHENOMENA, Vol: 294, Pages: 37-42, ISSN: 0167-2789

JOURNAL ARTICLE

Grolet A, Hoffmann NP, Schwingshackl C, 2015, Solitons in Non-Linear Cyclic Systems, Euromech Colloquium 573: Coupling and Nonlinear Interactions in Rotating Machinery

CONFERENCE PAPER

Kruse S, Tiedemann M, Zeumer B, Reuss P, Hetzler H, Hoffmann Net al., 2015, The influence of joints on friction induced vibration in brake squeal, JOURNAL OF SOUND AND VIBRATION, Vol: 340, Pages: 239-252, ISSN: 0022-460X

JOURNAL ARTICLE

Kruse S, Tiedemann M, Zeumer B, Reuss P, Hetzler H, Hoffmann Net al., 2015, The influence of joints on friction induced vibration in brake squeal (vol 340, pg 239, 2014), JOURNAL OF SOUND AND VIBRATION, Vol: 351, Pages: 311-312, ISSN: 0022-460X

JOURNAL ARTICLE

Peric R, Hoffmann N, Chabchou A, 2015, Initial wave breaking dynamics of Peregrine-type rogue waves: A numerical and experimental study, EUROPEAN JOURNAL OF MECHANICS B-FLUIDS, Vol: 49, Pages: 71-76, ISSN: 0997-7546

JOURNAL ARTICLE

Tiedemann M, Kruse S, Hoffmann N, 2015, Dominant damping effects in friction brake noise, vibration and harshness: the relevance of joints, PROCEEDINGS OF THE INSTITUTION OF MECHANICAL ENGINEERS PART D-JOURNAL OF AUTOMOBILE ENGINEERING, Vol: 229, Pages: 728-734, ISSN: 0954-4070

JOURNAL ARTICLE

Akhmediev N, Soto-Crespo JM, Devine N, Hoffmann NPet al., 2014, Rogue waves of the Sasa-Satsuma equation in a chaotic wave field

CONFERENCE PAPER

Akhmediev N, Soto-Crespo JM, Devine N, Hoffmann NPet al., 2014, Rogue waves of the Sasa-Satsuma equation in a chaotic wave field

CONFERENCE PAPER

Chabchoub A, Kimmoun O, Branger H, Kharif C, Hoffmann N, Onorato M, Akhmediev Net al., 2014, Gray solitons on the surface of water, PHYSICAL REVIEW E, Vol: 89, ISSN: 2470-0045

JOURNAL ARTICLE

Chabchoub A, Peric R, Hoffmann NP, 2014, DYNAMICS OF UNSTABLE STOKES WAVES: A NUMERICAL AND EXPERIMENTAL STUDY, 33rd ASME International Conference on Ocean, Offshore and Arctic Engineering, Publisher: AMER SOC MECHANICAL ENGINEERS

CONFERENCE PAPER

Gräbner N, Tiedemann M, Von Wagner U, Hoffmann Net al., 2014, Nonlinearities in Friction Brake NVH - Experimental and Numerical Studies

Copyright © 2014 SAE International. Industry and academia agree that brake squeal is a nonlinear phenomenon. Consequently, using solely linear finite-element (FE) models and assessing the tendency of a brake system to squeal exclusively on the stability of the trivial solution is not appropriate. However, the latter approach - in the brake community known as complex eigenvalue analysis (CEA) - is extensively used in industry. Until now, nonlinear simulation approaches considering existence and stability of periodic solutions are mostly limited to minimal models. Among the variety of reasons for this the complexity of large-scale nonlinear models as well as the identification of nonlinear material and system parameters are crucial. This contribution discusses the relevance of nonlinearities in friction brake noise, vibration, harshness (NVH) and presents a novel simulation approach for brake squeal. On the basis of experimental results it is pointed out that the consideration of nonlinearities in simulation as well as new methods for numerical studies are necessary to cope with the system-inherent phenomena. After presenting experimental methods to characterize nonlinearities in brake systems, a novel simulation approach for brake squeal is introduced. This approach is based on subspace projection and allows the calculation of limit cycles considering nonlinearities such as joint damping. Studies are conducted for minimal models and a full-scale industrial FE model.

CONFERENCE PAPER

Hadjihosseini A, Peinke J, Hoffmann NP, 2014, Stochastic analysis of ocean wave states with and without rogue waves, NEW JOURNAL OF PHYSICS, Vol: 16, ISSN: 1367-2630

JOURNAL ARTICLE

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